Effects of walking in nature on brain function and mood

The study of how physical environments shape human cognitive functioning and neurobiology has crystallized into the interdisciplinary field of environmental neuroscience. Historically, the restorative effects of natural environments were quantified through subjective psychological assessments, behavioral observations, and self-reported mood inventories. However, advancing neuroimaging technologies - ranging from high-resolution functional Magnetic Resonance Imaging (fMRI) to wearable mobile Electroencephalography (EEG) and functional Near-Infrared Spectroscopy (fNIRS) - have enabled researchers to map the precise neurobiological changes that occur when humans are exposed to, or actively navigate, natural settings ¹²²³⁴.

The empirical data indicates a profound disparity between how the human brain processes complex urban spaces compared to wild nature, curated green spaces, and aquatic blue spaces. Urban living is an established risk factor for mental health disorders, correlating with up to a 56% increase in mood and anxiety disorders and accounting for more than 30% of schizophrenia incidence globally ⁵. In contrast, exposure to nature induces measurable acute state changes in affective and cognitive neural networks, alongside emerging evidence of structural neuroplasticity ⁶⁷⁸⁹. This report exhaustively details the theoretical frameworks, measurement modalities, electrophysiological signatures, hemodynamic responses, and cross-cultural variables associated with walking in natural environments.

Theoretical Foundations of Environmental Neuroscience

The neurobiological investigation of nature exposure is primarily grounded in two foundational, complementary psychological theories. These frameworks serve as the theoretical basis for formulating hypotheses regarding which specific brain regions and large-scale networks should activate or deactivate during natural versus urban immersion.

Attention Restoration Theory and Cognitive Resource Replenishment

Attention Restoration Theory (ART), initially developed by environmental psychologists Rachel and Stephen Kaplan in the late 1980s, posits that cognitive processing in urban environments heavily taxes a finite mental resource known as "directed attention" ^51011121314. Drawing on William James's early distinctions between voluntary and involuntary attention, ART suggests that directed (voluntary) attention requires effortful, top-down cognitive control to suppress external distractions - such as traffic, digital stimuli, and dense crowds - and maintain goal-oriented focus ¹²¹⁴. Over time, the continuous expenditure of directed attention leads to cognitive fatigue, characterized by diminished executive functioning, increased impulsivity, impaired problem-solving, and elevated irritability ¹²¹⁴¹⁶.

ART asserts that natural environments possess a distinct perceptual quality termed "soft fascination" ^312131617. Soft fascination involves engaging with stimuli that are inherently interesting but not overwhelmingly demanding - such as rustling leaves, fractal branch patterns, drifting clouds, or flowing water. These stimuli effortlessly capture bottom-up, involuntary attention ⁵¹²¹⁴. Because involuntary attention does not drain cognitive reserves, the directed attention system, largely mediated by the prefrontal cortex, is allowed to rest and replenish ^1213141715.

According to ART, a truly restorative environment must possess four specific properties: 1. Being Away: Psychological or physical distance from routine demands and stressors. 2. Extent: Sufficient scope, scale, and coherence to invite immersive exploration without confusion. 3. Fascination: The presence of engaging but undemanding stimuli (soft fascination), contrasting with the "hard fascination" of highly stimulating events like sporting matches or intense media. 4. Compatibility: A resonance between the affordances of the environment and the individual's current inclinations or purposes ¹²¹⁴¹⁵.

Stress Reduction Theory and Evolutionary Biophilia

In contrast to ART's cognitive focus, Stress Reduction Theory (SRT), proposed by Roger Ulrich, centers on the affective and physiological pathways of environmental restoration ^51011161718. Grounded in evolutionary psychology and closely related to the Biophilia Hypothesis - which suggests an innate human drive to affiliate with living systems - SRT argues that humans have evolved to experience immediate, unconscious, positive affective responses to unthreatening natural landscapes ^35111416.

According to SRT, viewing environments that historically signaled survival advantages (e.g., lush vegetation, clean water sources, open vistas providing a vantage point) triggers a rapid reduction in physiological arousal. This involves an immediate decrease in sympathetic nervous system activity (the "fight-or-flight" response) and a concomitant increase in parasympathetic tone, resulting in lower blood pressure, reduced heart rate, decreased skin conductance, and lower circulating cortisol levels ^516171920. In Ulrich's framework, cognitive improvements are primarily viewed as secondary byproducts of this primary physiological and emotional relaxation, rather than the central mechanism of restoration ¹⁴¹⁷¹⁸.

Theoretical Integration and Multi-Phasic Models

While historically viewed as competing models, contemporary environmental neuroscience predominantly treats ART and SRT as describing interconnected, sequential processes ¹⁴¹⁷¹⁸. A multi-phasic model of restoration suggests that exposure to nature first initiates a rapid SRT-mediated affective and physiological relaxation. This autonomic down-regulation subsequently establishes the baseline neurochemical conditions necessary for the ART-mediated recovery of high-level cognitive resources ¹⁴¹⁷.

Neuroimaging Modalities in Naturalistic Environments

Historically, investigating the brain's response to environmental stimuli required static, laboratory-bound measurements. Participants were forced to view images or virtual reality simulations of nature while immobilized inside scanners, limiting the ecological validity of the findings ^22212223. Recent technological advancements have enabled the deployment of mobile neuroimaging modalities, allowing researchers to capture real-time neural activity while participants physically navigate natural and urban terrains ^122422242529.

Functional Magnetic Resonance Imaging

Functional Magnetic Resonance Imaging (fMRI) provides exceptional spatial resolution, allowing researchers to observe deep subcortical structures involved in emotion, stress processing, and memory - most notably the amygdala and the hippocampus ^4583026. However, fMRI measures neural activity indirectly via the blood-oxygen-level-dependent (BOLD) hemodynamic response, which operates on a delay of several seconds compared to actual neuronal firing ²¹. Because an fMRI machine is an immobile, highly sensitive magnetic cylinder, it is impossible to record continuous data during an outdoor walk. Consequently, environmental neuroscience studies utilizing fMRI strictly employ pre- and post-walk experimental designs, assessing residual neural changes after the exposure has concluded ⁵⁶⁷⁸²⁶.

Mobile Electroencephalography

Electroencephalography (EEG) offers a direct measure of postsynaptic electrical activity with exceptional temporal precision, capturing neural oscillations on the order of milliseconds ^221252728. The development of mobile EEG (mEEG) systems has revolutionized environmental neuroscience by allowing portable, real-time recording in the field ^{22224252927282930}.

However, a major historical limitation of utilizing EEG during whole-body movement is the poor signal-to-noise ratio. The amplitude of recorded electrocortical signals is minute and frequently obscured by massive motion and myoelectric (muscle) artifacts generated by walking, head movement, and foot strikes ²⁴²⁷²⁸. Advances in independent component analysis (ICA) and real-time artifact rejection algorithms have increasingly made it possible to isolate high-fidelity data reflecting true neural oscillations as an individual actively walks through a forest or an urban street ²⁴²⁷²⁸.

Functional Near-Infrared Spectroscopy

Functional Near-Infrared Spectroscopy (fNIRS) bridges the methodological gap between fMRI and EEG. It utilizes near-infrared light emitted into the scalp to detect concentration changes in oxygenated (HbO) and deoxygenated hemoglobin (HbR) in the cortical surface layer ^3031323334. Like fMRI, it relies on neuro-vascular coupling to infer brain activity, but unlike fMRI, fNIRS devices are lightweight, portable, and highly tolerant of motion artifacts ^30313435.

This modality is exceptionally well-suited for monitoring Prefrontal Cortex (PFC) activation during dynamic, real-world navigation. It reveals the specific metabolic costs of processing complex urban environments versus natural landscapes without confining the participant ^323334353637. However, due to the limited penetration depth of near-infrared light (typically following a curved "banana-shaped" path through the scalp and skull), fNIRS cannot measure activity in deep brain structures like the amygdala ²³¹³⁴.

Electrophysiological Signatures of Nature Walking

Through the application of stationary and mobile EEG, researchers have identified specific frequency band modulations that act as reliable neural signatures of nature exposure. These electrophysiological markers provide objective evidence of the cognitive and affective shifts proposed by ART and SRT.

Alpha Oscillations and Visual Engagement

Alpha band activity (8 - 13 Hz) has emerged as the most robust and consistent neurophysiological marker of nature exposure ^12212328. Alpha oscillations are generally inversely correlated with cortical arousal; higher alpha power indicates a state of wakeful relaxation and a reduced information processing load ²³²⁸⁴³. The vast majority of environmental EEG studies report significant increases in generalized alpha power following exposure to natural environments or stimuli ^1234338.

Specifically, research targeting parietal alpha power has revealed distinct differences in visual engagement between nature and urban scenes. Studies have shown that viewing nature images decreases high-alpha band activity (11 - 13 Hz) while increasing low-alpha activity (8 - 10 Hz) ²²¹. This bifurcation suggests that nature engages bottom-up visual attention in a manner that is engaging but inherently relaxing, fitting the precise profile of "soft fascination" described by ART ²²¹.

Frontal Midline Theta and Executive Cognitive Strain

Theta band oscillations (4 - 8 Hz), particularly Frontal Midline Theta (FMθ), provide deep insights into the strain placed on the directed attention system ^221292839. FMθ is an established neural signature of attention and cognitive effort, thought to reflect neural activity originating in the dorsal anterior cingulate cortex (dACC) - a region heavily implicated in cognitive control and conflict monitoring ³⁹. FMθ power characteristically increases in response to heightened task difficulty, cognitive load, and the need for sustained executive attention ³⁹.

In randomized controlled trials utilizing pre- and post-walk EEG assessments, researchers found that participants engaging in a 40-minute urban walk exhibited significantly greater FMθ activity compared to those completing an identical duration walk in nature ²³⁹⁴⁰. The urban environment - characterized by the need to navigate heavy traffic, avoid pedestrians, and process high volumes of artificial visual stimuli - forces the brain into a state of continuous information filtering, thus elevating FMθ ³⁹. Conversely, the significantly lower FMθ observed following the nature walk serves as a distinct neural mechanism demonstrating the attentional rest and restoration predicted by ART ²⁹³⁹.

Beta Band Activity and Psychological Tension

Beta band activity (13 - 30 Hz) is traditionally associated with active concentration, alert wakefulness, and motor behavior ^1223841. Higher frequencies within the beta range are also heavily correlated with states of psychological stress, anxiety, and heightened tension ²²³⁸. Exposure to nature, whether through physical walking or virtual immersion, reliably induces reductions in beta power, reflecting a clear decrease in cognitive load and psychological stress ³²²³⁸.

Complex Ratios and Affective Asymmetry

Researchers also utilize composite EEG metrics to assess the walking experience. The Theta/Beta Power Ratio (TBR) is an established index of cognitive load. Studies show that natural environments evoke a lower TBR compared to crowded urban spaces, implying enhanced mind-wandering in nature and rigid, strained attentional control in cities ²⁹⁴⁰. Furthermore, Frontal Alpha Asymmetry (FAA) - a metric where greater left frontal activity indicates approach-oriented positive affect and right frontal activity indicates withdrawal or negative affect - shows complex variations based on crowding. While nature generally promotes positive valence, some mobile EEG studies note that FAA can be higher when successfully navigating crowded urban outdoors compared to standing still, suggesting that the sense of control during active walking modulates affective states ²⁹.

Hemodynamic and Network-Level Brain Responses

While EEG maps the high-speed timing of electrical states, hemodynamic imaging (fMRI and fNIRS) is required to identify the precise cortical and subcortical anatomical structures driving the restorative cascade during and after nature exposure.

Amygdala Regulation and Stress Processing

The amygdala is a subcortical structure serving as the brain's primary locus for processing fear, threat detection, and emotional stress ⁵⁸²⁶. In a landmark 2022 study by the Lise Meitner Group for Environmental Neuroscience, researchers established a definitive causal link between nature exposure and acute neurobiological stress reduction ⁵⁸. Participants underwent fMRI scanning before and after a 60-minute walk in either a wild forest (Grunewald, Berlin) or a busy commercial shopping street with heavy traffic ⁵⁸.

The results demonstrated a significant decrease in amygdala activity following the forest walk, indicating that nature elicits a rapid, beneficial down-regulation of stress-processing centers ⁵⁸²⁶⁴⁸. Notably, amygdala activity in the urban walking group remained stable but did not increase. This argues against the commonly held view that a single urban walk inherently causes an acute spike in stress, suggesting instead that wild nature actively repairs and buffers stress levels below baseline ⁸. This down-regulation provides robust neurobiological validation for Ulrich's Stress Reduction Theory ⁵¹⁶¹⁷.

Prefrontal Cortex Dynamics and Rumination

The Prefrontal Cortex (PFC) is the seat of executive function, working memory, and complex decision-making. Utilizing fNIRS, researchers have monitored PFC oxygenation levels (HbO) in real-time as participants navigate different environments ^303132333436. Viewing pleasant natural environments or walking in green spaces leads to a significant decrease in HbO concentrations in the central and right regions of the PFC, a metabolic indicator of physiological relaxation and reduced cognitive demand ³³³³⁶.

Furthermore, specific sub-regions of the PFC respond uniquely to nature. A seminal 2015 fMRI study published in PNAS found that a 90-minute nature walk decreased activity specifically in the subgenual prefrontal cortex (sgPFC) ³¹⁷⁴⁹. The sgPFC is closely linked to rumination - a pattern of repetitive, negative, self-referential thought that is a core feature of depression and anxiety disorders ¹⁷⁴⁹. The reduction of sgPFC activity, coupled with decreased self-reported rumination on psychological questionnaires, demonstrates nature's capacity to disrupt maladaptive cognitive loops ⁶¹⁷⁴⁹.

Default Mode Network Integration and Associative Thought

The Default Mode Network (DMN) - comprising a constellation of brain regions including the medial prefrontal cortex, posterior cingulate cortex, and angular gyrus - is highly active when the brain is at wakeful rest and not engaged in externally directed, goal-oriented tasks. It is the network responsible for mind-wandering, autobiographical memory recall, and creative association ^312131617. In modern urban environments, continuous demands for directed attention suppress DMN activity, locking the brain into the central executive network to handle the high stimulus load ¹³¹⁶.

Walking in nature fundamentally alters this dynamic. Because natural environments engage "soft fascination" without demanding heavy cognitive filtering, they do not monopolize cognition ^12131617. This environment provides the central executive network with metabolic relief while allowing the DMN to gently activate ¹³¹⁶. Neuroimaging reveals that during nature exposure, the DMN exhibits enhanced functional connectivity with visual and attentional networks ³¹²¹³. This integration creates a rare neurological state where focused attention and internal reflection work harmoniously rather than in opposition ¹³. This DMN synchronization is theorized to be the precise neurological mechanism underlying the bursts of divergent thinking, insight, and mental clarity frequently reported during nature walks ¹³¹⁶¹⁷.

Structural Neuroplasticity and Morphological Adaptation

While the acute state changes measured by EEG and fNIRS resolve relatively rapidly, sustained or profound environmental exposure can induce structural neuroplasticity - physical, measurable alterations in the volume and density of brain tissue ⁶⁷⁴²⁴³.

Epidemiological neuroimaging studies have previously demonstrated that lifelong exposure to rural, green environments is correlated with distinct gray matter density differences when compared to urban populations. Specifically, strong negative correlations have been found between early-life urbanicity and gray matter volumes in the right dorsolateral prefrontal cortex and the perigenual anterior cingulate cortex (pgACC) - regions crucial for stress regulation and associated with long-term schizophrenia risk ⁹.

Hippocampal Volume and the Subiculum

More remarkably, recent longitudinal and interventional research suggests that structural changes may not strictly require lifelong exposure. A 2024 study investigated hippocampal brain plasticity using high-resolution MRI before and after a single one-hour walk ⁶⁷²⁶. The hippocampus is highly sensitive to spatial navigation, environmental context, and circulating stress hormones ⁶⁷¹⁷⁴⁴.

The researchers found that participants who walked in the forest exhibited a volumetric increase in the subiculum - a specific hippocampal subfield that acts as the primary output of the hippocampus and is critically involved in the inhibition of the stress response via the HPA axis ⁶⁷²⁶⁴⁴. This rapid volume increase was directly correlated with a decrease in self-reported rumination among participants ⁶²⁶.

Methodological Constraints and Calibrated Uncertainty

It is necessary to contextualize the findings regarding acute structural plasticity. While the discovery of rapid subiculum enlargement following a one-hour walk is a groundbreaking indicator of environmental neuroplasticity, the researchers explicitly noted that the statistical interaction did not withstand the highly conservative Bonferroni correction for multiple comparisons ⁶²⁶. Therefore, while the data strongly suggests rapid morphological adaptation to natural environments, calibrated uncertainty is required. Further large-scale, pre-registered replications are necessary to confirm whether a single hour of exposure causes durable structural plasticity, or if the observed volumetric changes represent transient fluid shifts within the neural tissue ⁶⁷²⁶.

Differentiation of Environmental Variables

Research indicates that not all non-urban environments exert identical neurological effects. The specific structural, visual, and auditory features of the environment directly dictate the magnitude and quality of the restorative response.

Urban Green Spaces Versus Wild Forests

While curated urban parks provide undeniable health benefits compared to concrete city streets, wild or uncurated forests consistently yield superior restorative neurological outcomes ^12534546. The high visual complexity, biodiversity, and total lack of man-made visual intrusions in wild nature maximize soft fascination and minimize the need for directed attention ^512131416. Furthermore, the auditory landscape of wild nature - completely devoid of low-frequency traffic noise - increases functional brain connectivity and reduces global brain entropy, variables that heavily manicured urban parks struggle to replicate fully due to their proximity to urban noise pollution ^14534546.

The Neurological Impact of Aquatic Blue Spaces

Environments featuring prominent water bodies - referred to in the literature as "blue spaces" - have emerged as highly potent neurological modulators. Recent meta-analyses and real-time EEG studies suggest that blue spaces may elicit an even stronger restorative response than purely green spaces ^{323385647484950}.

In a comparative EEG study evaluating street spaces, open green spaces, and varying types of blue spaces, researchers found that dynamic aquatic environments (specifically categorized as "Falling bluespace," such as waterfalls or rushing streams) yielded the absolute highest levels of restorative alpha brainwaves and the lowest levels of stress-associated beta brainwaves ³⁸. The gentle, rhythmic visual and auditory patterns of moving water represent an optimal stimulus for effortless involuntary attention, capturing the sensory apparatus without placing any demands on executive function ¹⁶³⁸⁴⁸.

Fractal Geometry and Perceptual Fluency

A unifying feature of highly restorative green and blue spaces is the heavy presence of natural fractals. Fractals are geometric patterns that self-repeat at multiple scales, observable in the branching of tree limbs, the shapes of clouds, the distribution of leaves, and the contours of coastlines ³¹⁶⁵¹.

The human brain has evolved over hundreds of thousands of years to process these specific mathematical patterns with immense efficiency, a concept known as visual fluency. Neuro-aesthetic research demonstrates that the human brain detects the presence of natural fractals in a mere 50 milliseconds ⁵¹. This incredibly rapid detection bypasses conscious cognitive appraisal, immediately triggering a cascade of autonomic relaxation responses ¹⁶¹⁷⁵¹. Studies show that viewing natural fractals can reduce observer stress and mental fatigue by up to 60%, providing a precise, mathematically grounded geometrical explanation for the neurobiological mechanics of Stress Reduction Theory ⁵¹.

Cross-Cultural Perspectives on Nature Immersion

The most robust and voluminous body of literature regarding the physiological and endocrinological impact of nature immersion stems from Japan and South Korea, centered around the formal practice of Shinrin-yoku (forest bathing). Coined by the Japanese Ministry of Agriculture, Forestry, and Fisheries in 1982, Shinrin-yoku is an immersive, multi-sensory therapeutic practice that has been widely integrated into Japanese public health and preventive medicine ^{19204952536454555657585971}.

Physiological Outcomes of Shinrin-yoku in Asian Populations

Extensive field experiments conducted across dozens of Japanese forests demonstrate that Shinrin-yoku potently suppresses the Hypothalamic-Pituitary-Adrenal (HPA) axis and the sympathetic nervous system ^1949525771. Compared to walking in urban environments, forest bathing consistently lowers salivary cortisol concentrations, reduces pulse rate, lowers both systolic and diastolic blood pressure, and boosts the activity of Natural Killer (NK) immune cells ^192049526471. Remarkably, the immune and autonomic benefits generated by a multi-day forest bathing trip have been shown to persist for up to 30 days post-exposure ⁴⁹⁵²⁷¹.

Cultural Familiarity and Cognitive Construal Differences

While the fundamental neurological architecture responding to natural fractals and biophilic elements is universally human, the magnitude and qualitative experience of restoration can be modulated by cultural familiarity and deeply ingrained social schemas ^536061626364. The concept of what constitutes a "restorative" natural environment is not entirely objective ⁶².

In Japan, Shinrin-yoku is deeply embedded in a cultural framework that emphasizes mindfulness, introspection, sensory immersion in silence, and a philosophical harmony with nature ⁵⁸⁵⁹⁷¹. When these exact interventions are exported to Western (WEIRD: Western, Educated, Industrialized, Rich, Democratic) populations, the efficacy can vary. For instance, studies in the UK applying strict forest bathing protocols observed reduced efficacy, partly due to climatic deterrents, but also owing to a cultural lack of familiarity with the concept of deliberate, static, silent nature immersion as a medical intervention ⁵³⁶². Western applications of forest bathing tend to require more active, flexible, and socially engaged adaptations to achieve high compliance and restorative outcomes ⁵⁸.

Furthermore, cross-cultural neuroimaging and psychological research indicates that cognitive styles - such as the independent self-construal prevalent in the West versus the interdependent self-construal prevalent in East Asia - can fundamentally alter how the brain allocates attention to contextual backgrounds and appraises environmental threat ^61656667. Japanese participants often report different baseline evaluations of interpersonal stress and exhibit subtle differences in left superior temporal gyrus (STG) tuning to culturally congruent emotional cues compared to Western cohorts ⁶⁴⁶⁶. Consequently, an environment or specific natural feature (e.g., willow trees) perceived as highly restorative and harmonious by one demographic might be processed differently by another based on learned visual schemas and cultural associations ^2616264.

Clinical Implications and Public Health Applications

The accumulation of rigorous neurobiological and electrophysiological evidence has profound implications for clinical psychology, psychiatric rehabilitation, and modern urban planning. The identification of objective, reproducible changes in brain function validates "nature prescriptions" as a legitimate, evidence-based adjunctive therapy for various psychiatric conditions ¹⁶⁴⁵⁷.

Nature-Based Interventions for Affective Disorders

For individuals diagnosed with Major Depressive Disorder (MDD), walking in nature has been proven to yield significant cognitive and affective benefits that bypass standard emotional deficits. In controlled clinical trials, individuals with MDD were explicitly asked to ruminate on a painful, unresolved autobiographical event prior to taking a 50-minute walk in either an urban or natural setting. Despite the induced rumination, the nature walk resulted in significant improvements in short-term memory capacity (exhibiting a large statistical effect size) and elevated positive mood ⁶⁹⁶⁸. This recovery profile was completely absent in the urban control group, demonstrating that the environmental context can physically override internal depressive rumination by drawing on involuntary attention pathways ⁴⁹⁶⁸.

Urban Planning and Green Infrastructure

At the population level, the neurological penalties of urban living - ranging from constant executive attention fatigue (high FMθ) to chronic amygdala hyperactivity and suppressed DMN connectivity - necessitate a fundamental reevaluation of city design ^5893953. Incorporating high-density green infrastructure, accessible blue spaces, and architectural fractal geometries into urban environments is not merely an aesthetic preference; it is a vital public health intervention ^4846564951.

By creating environments that organically trigger the neurobiological cascade of Stress Reduction Theory and Attention Restoration Theory, urban planners can actively buffer the neurological toll of modern urbanization, reducing the incidence of stress-related mental health disorders and fostering cognitive resilience across populations ⁸⁹⁴⁷⁴⁹.